Monday, August 25, 2008

Hurricane Watch: Gustav Develops Fast

From Wunderblog:

Tropical Storm Gustav intensified rapidly from a mere disturbance to a strong tropical storm in just a few short hours....

...The track forecast for GustavThe models have come into better agreement on the future track of Gustav. Gustav is likely to continue northwest across the southwestern peninsula of Haiti, and is being drawn this direction by a trough of low pressure currently exiting the U.S. East Coast. By Wednesday, the trough is expected to move eastward, leaving Gustav in a region of weak steering currents. The storm will slow down, and is then expected to turn westward, or even slightly south of west, as a ridge of high pressure builds in, forcing Gustav to move parallel to Cuba. The outlier model is the NOGAPS, which takes Gustav northward through the Bahamas and parallel to the U.S. East Coast. For now, I am discounting this solution. The NOGAPS was also the outlier model during Fay, and consistently made the worst track forecasts among the major models. I expect Gustav to track over or just south of Cuba. As Gustav nears western Cuba on Friday, another trough of low pressure moving across the central U.S. may be strong enough to turn Gustav northward, into the Gulf of Mexico. This is the solution given by the GFDL, HWRF, and ECMWF models, which foresee a Category 1 or 2 hurricane just west of Key West, Florida, on Saturday. The GFS, UKMET, and Canadian models disagree, and forecast that the new trough of low pressure will not be strong enough to turn Gustav to the north. Instead, these models predict that Gustav will continue west into the Yucatan Peninsula.

Which set of models do you trust? Both solutions are plausible. I plotted up the errors for some of the computer model forecasts made during Fay. While Fay was over Hispaniola and Cuba, the GFDL model made the best track forecasts, among the four main models used by NHC: GFS, GFDL, NOGAPS, and UKMET. This makes me more inclined to trust the GFDL model's forecasts for Gustav, since Fay and Gustav are similar storms....MORE